ESEEM studies at 7.8, 9.5, and 10.8 GHz were initiated in order to investigate the ligand structure and charge symmetry of the high and low pH forms of the protein. ESEEM spectra suggest that there are two imidazoles coordinated to copper, with coupling to two nitrogens (a measure of spin delocalization for the Cu d9 configuration) differing. The ESEEM spectra of high and low pH forms of the protein are qualitatively identical. However, the change of width in combination lines of the spectrum indicate reorganization of relative geometry of the two imidazoles at elevated pH. There is no indication of a new ligands at high pH. Furthermore, the quadrupole parameters of the remote imidazole nitrogen atoms are unchanged. The only apparent difference between the two proteins is the magnitude of the nuclear hyperfine coupling, which seems to be less in the high pH form of the protein. A paper on the Rhus stellacyanin has been accepted for